Search

We report a new, rare detection of H I 21 cm absorption associated with a quasar (only six quasars are known at 1 < z < 2) toward J2339−5523 at zem = 1.3531, discovered through the MeerKAT Absorption Line Survey (MALS). The absorption profile is broad (∼400 km s−1), and the peak is redshifted by ∼200 km s−1 from zem. Interestingly, optical/far-UV spectra of the quasar from the Magellan-MIKE/HST-COS spectrographs do not show any absorption features associated with the 21 cm absorption, despite the coincident presence of the optical quasar and the radio core inferred from a flat-spectrum component with a flux density of ∼65 mJy at high frequencies (> 5 GHz). The simplest explanation would be that no large H I column (N(H I) > 1017 cm−2) is present toward the radio core and the optical active galactic nucleus. Based on the joint optical and radio analysis of a heterogeneous sample of 16 quasars (zmedian = 0.7) and 19 radio galaxies (zmedian = 0.4) with H I 21 cm absorption detection and matched in 1.4 GHz luminosity (L1.4 GHz), a consistent picture emerges according to which quasars primarily trace the gas in the inner circumnuclear disk and cocoon created by the interaction of the jet with interstellar medium. They (i.e., quasars) exhibit a L1.4 GHz – ΔVnull correlation and a frequent mismatch of the radio and optical spectral lines. The radio galaxies show no such correlation and likely trace the gas from the cocoon and the galaxy-wide interstellar medium outside the photoionization cone. The analysis presented here demonstrates the potential of radio spectroscopic observations to reveal the origin of the absorbing gas associated with active galactic nuclei that may be missed in optical observations. [ABSTRACT FROM AUTHOR]

present composite spectra constructed from a sample of 242 150 Lyman a (Lyα) forest absorbers at redshifts 2.4 < z < 3.1 identified in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of the Sloan Digital Sky Survey III. We select forest absorbers by their flux in bins 138 km s-1 wide (approximately the size of the BOSS resolution element). We split these absorbers into five samples spanning the range of flux -0.05 ≤ F < 0.45. Tests on a smaller set of high-resolution spectra show that our three strongest absorption samples would probe circumgalactic regions (projected separation

We probe the small-scale absorption line variability using absorption depth based analysis of a sample of 64 ultra-fast outflow (UFO) C  iv broad absorption line (BAL) quasars monitored using the Southern African Large Telescope. We confirm the strong monotonic increase in the strength of variability with increasing outflow velocity. We identify regions inside the BAL trough for each source where the normalized flux difference between two epochs is >0.1 for a velocity width ≥500 km s−1 (called 'variable regions'). We find that the total number of variable regions increases with the time interval probed and the number of BALs showing variable regions almost doubles from short (<2 yr) to long (>2 yr) time-scales. We study the distributions of variable region properties such as its velocity width, depth, and location. These regions typically occupy a few-tenths of the entire width of the BAL. Their widths are found to increase with increasing time-scales having typical widths of ∼2000 km s−1 for Δ t > 2 yr. However, their absolute velocity with respect to z em and their relative position within the BAL profile remain random irrespective of the time-scale probed. The equivalent width variations of the BALs are strongly dependent on the size and depth of the variable regions but are little dependent on their total number. Finally, we find that ∼17 per cent of the UFO BALs show uncorrelated variability within the BAL trough. [ABSTRACT FROM AUTHOR]

We study the time variability (over ≤7.3 yr) of ultra fast outflows (UFOs) detected in a sample of 64 C iv broad absorption line (BAL) quasars (with 80 distinct BAL components) monitored using the Southern African Large Telescope. By comparing the properties of the quasar in our sample with those of a control sample of non-BAL quasars, we show that the distributions of black hole mass are different and the bolometric luminosities and optical photometric variations of UFO BAL quasars are slightly smaller compared to that of non-BAL quasars. The detection fraction of C  iv equivalent width (W) variability (∼95 per cent), the fractional variability amplitude |$\left(\frac{\Delta W}{W}\right)$| and the fraction of 'highly variable' BAL (i.e. |$\big|$| |$\frac{\Delta W}{W}$| |$\big|$| > 0.67) components (∼33 per cent) are higher in our sample compared to the general BAL population. The scatter in |$\frac{\Delta W}{W}$| and the fraction of 'highly variable' BALs increase with the time-scale probed. The |$\frac{\Delta W}{W}$| distribution is asymmetric at large time scales. We attribute this to the BAL strengthening time-scales being shorter than the weakening time-scales. The BAL variability amplitude correlates strongly with the BAL properties compared to the quasar properties. BALs with low W, high-velocity, shallow profiles, and low-velocity width tend to show more variability. When multiple BAL components are present, a correlated variability is seen between low- and high-velocity components with the latter showing a larger amplitude variations. We find an anticorrelation between the fractional variations in the continuum flux and W. While this suggests photoionization induced variability, the scatter in continuum flux is much smaller than that of W. [ABSTRACT FROM AUTHOR]

The chemical composition of gas in galaxies can be measured in great detail using absorption spectroscopy. By studying gas in galaxies in this way, it is possible to investigate small and faint galaxies, which are the most numerous in the universe. In particular, the chemical distribution of gas in absorbing systems gives us insight into cycles of gas in and around galaxies. In this work we study chemical enrichment within 64 damped Lyman- absorption systems (DLAs) for redshifts in the range 1:7 < z < 4:2. We use high-resolution spectra from VLT/UVES to infer dust depletion from relative abundances of several metals. Specifically, we performed a componentby- component analysis within DLAs, and characterised variations in their chemical enrichment. Unlike hydrogen, the metal columns can be characterised according to their individual components. We used them to derive the dust depletion, which is an indicator of chemical enrichment. Our main results are as follows. Firstly, we find that some DLAs are chemically diverse within themselves (with the measure of dust depletion [Zn/Fe]fit ranging up to 0.62 dex within a single system), suggesting that the absorbing gas within these galaxies is chemically diverse. Secondly, although we do not find a clear trend of decreasing dust depletion with redshift, we do see that the most chemically enriched systems are at lower redshifts. We also observe evidence for dust-poor components at all redshifts, which may be due to the accretion of pristine gas onto galaxies. By combining the chemical and kinematic properties of the individual gas components, we observe potential signatures of infalling gas with low depletion at velocities below ~100 km s1, and outflows with high depletion and velocities of ~600 km s1. Finally, we find over-abundances of -elements (an enhancement of ~0.3 dex) and under-abundances of Mn in several gas components, which is likely a signature of core-collapse supernovae nucleosythesis in the ISM. We observe these effects mostly at lower levels of chemical enrichment. [ABSTRACT FROM AUTHOR]

The BL Lac object PKS 1413+135 was observed by the Large Survey Project MeerKAT Absorption Line Survey (MALS) in the L-band, at 1139 MHz and 1293–1379 MHz, targeting the H I and OH lines in absorption at z = 0.24671. The radio continuum might come from the nucleus of the absorbing galaxy or from a background object at redshift lower than 0.5, as suggested by the absence of gravitational images. The H I absorption line is detected at a high signal-to-noise ratio, with a narrow central component, and with a red wing, confirming previous results. The OH 1720 MHz line is clearly detected in (maser) emission, peaking at a velocity shifted by −10 to −15 km s−1 with respect to the H I peak. The 1612 MHz line is lost due to radio frequency interference. The OH 1667 MHz main line is tentatively detected in absorption, but not the 1665 MHz line. Over 30 years a high variability is observed in optical depths, due to the rapid changes of the line of sight caused by the superluminal motions of the radio knots. The H I line has varied by 20% in depth, while the OH-1720 MHz depth has varied by a factor of ∼3. The position of the central velocity and the widths also varied. The absorbing galaxy is an early-type spiral (maybe S0) seen edge-on, with a prominent dust lane, covering the whole disk. Given the measured mass concentration and the radio continuum size at centimeter wavelengths (100 mas corresponding to 400 pc at z = 0.25), the width of the absorption lines from the nuclear regions are expected up to 250 km s−1. The narrowness of the observed lines (< 15 km s−1) suggests that the absorption comes from an outer gas ring, as frequently observed in S0 galaxies. The millimetric lines are even narrower (< 1 km s−1), which corresponds to the continuum size restricted to the core. The radio core is covered by individual 1 pc molecular clouds, whose column density is a few 1022 cm−2, which is compatible with the gas screen detected in X-rays. [ABSTRACT FROM AUTHOR]

We present MeerKAT Absorption Line Survey (MALS) observations of the H  i gas in the Klemola 31 galaxy group (z  = 0.029), located along the line of sight to the radio-loud quasar PKS 2020−370 (z  = 1.048). Four galaxies of the group are detected in H  i emission, and H  i absorption is also detected in front of PKS 2020−370 in Klemola 31A. The emission and absorption are somewhat compensating on the line of sight of the quasar, and the derived column density of the absorption appears underestimated, with respect to the neighbouring emission. A symmetric tilted-ring model of Klemola 31A, assuming the absorbing gas in regular rotation in the plane, yields a rather high spin temperature of 530 K. An alternative interpretation is that the absorbing gas is extra-planar, which will also account for its non-circular motion. The Na  i /Ca  ii ratio also suggests that the absorbing gas is unrelated to cold H  i disc. Two of the galaxies in the Klemola group are interacting with a small companion, and reveal typical tidal tails, and velocity perturbations. Only one of the galaxies, ESO 400−13, reveals a strong H  i deficiency, and a characteristic ram-pressure stripping, with a total asymmetry in the distribution of its gas. Since a small galaxy group as Klemola 31 is not expected to host a dense intra-group gas, this galaxy must be crossing the group at a very high velocity, mostly in the sky plane. [ABSTRACT FROM AUTHOR]

We present a time variability analysis of broad absorption lines (BAL; spread over the velocity range of 5800–29 000 km s−1) seen in the spectrum of J132216.25 + 052446.3 (z em = 2.04806) at ten different epochs spanning over 19 yr. The strongest absorption component (BAL-A; spread over 5800–9900 km s−1) is made up of several narrow components having velocity separations close to C  iv doublet splitting. The C  iv , N  v , and Si  iv absorption from BAL-A show correlated optical depth variability without major changes in the velocity structure. A very broad and shallow absorption (BAL-C; spread over the velocity range 15 000–29 000 km s−1) emerged during our monitoring period coinciding with a dimming episode of J1322 + 0524. All the identified absorption lines show correlated variability with the equivalent widths increasing with decreasing flux. This together with the C  iv emission line variability is consistent with ionization being the main driver of the correlated variability. The observed UV-continuum variations are weaker than what is required by the photoionization models. This together with a scatter in the C  iv equivalent width at a given continuum flux can be understood if variations of the C  iv ionizing photons are much larger than that of the UV continuum, the variations in the ionizing photon and UV fluxes are not correlated and/or the covering factor of the flow varies continuously. We suggest BAL-A is produced by a stable clumpy outflow located beyond the broad emission line region and BAL-C is a newly formed wind component located near the accretion disc and both respond to changes in the ionizing continuum. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of time variability of two distinct C  iv broad absorption line (BAL) components seen in the spectrum of J162122.54+075808.4 (z em = 2.1394) using observations from SDSS, NTT, and SALT taken at seven different epochs spanning about 15 yr. The blue-BAL component (with an ejection velocity, |$v_{\rm e}\sim 37\, 500$|  km s−1) is an emerging absorption that shows equivalent width variations and kinematic shifts consistent with acceleration. The red-BAL component (⁠|$v_{\rm e} \sim 15\, 400$|  km s−1) is a three-component absorption. One of the components is emerging and subsequently disappearing. The two other components show kinematic shifts consistent with acceleration coupled with equivalent width variability. Interestingly, we find the kinematic shifts and equivalent width variability of the blue- and red-BAL components to be correlated. While the C  iv emission-line flux varies by more than 17 per cent during our monitoring period, the available light curves (covering rest frame 1300–2300 Å) do not show more than a 0.1 mag variability in the continuum. This suggests that the variations in the ionizing flux are larger than that of the near-ultraviolet flux. However, the correlated variability seen between different BAL components cannot be explained solely by photoionization models without structural changes. In the framework of disc wind models, any changes in the radial profiles of density and/or velocity triggered either by disc instabilities or by changes in the ionizing radiation can explain our observations. High-resolution spectroscopic monitoring of J1621+0758 is important to understand the physical conditions of the absorbing gas and thereby to constrain the parameters of disc wind models. [ABSTRACT FROM AUTHOR]

We have searched high spectral resolution spectra of quasars known to exhibit high redshift (z > 1.7) intervening H2-bearing damped Lyman-α (DLA) systems for partial coverage of the quasar emission by intervening H2 clouds. Partial coverage manifests itself by the presence of non-zero residual flux in the core of saturated H2 absorption lines. The residual flux can be observed either only at the bottom of absorption lines redshifted on top of quasar emission lines, in which case part of the broad line region (BLR) is not covered, or in all absorption lines, in case some continuum source is not covered. Among 35 H2 absorption clouds in 14 quasar spectra obtained with the VLT-UVES or Keck-HIRES spectrographs, we detect partial coverage of the BLR for 13 clouds. This result suggests that the probability of partial coverage of the QSO BLR by a distant H2 absorption cloud is about 40 per cent. For four systems towards Q 0013−0029, Q 0405−4418, Q 0812+3208, and J 2100−0641, partial coverage is detected for the first time. We determine the theoretical probability of partial coverage of the BLR by a distant H2 cloud as a function of the ratio between the cloud and the BLR sizes. Using this model, we obtain an estimate of the characteristic BLR radius of |$50^{+19}_{-23}\,\rm{light \,days}$|⁠. This is similar to the estimate of the BLR size obtained by reverberation-mapping analysis |$({\sim}100\,\rm{light\, days})$|⁠. [ABSTRACT FROM AUTHOR]

We present results from spectroscopic observations with X-shooter at the Very Large Telescope of seven H2-bearing damped Lyman-α systems (DLAs) at high redshifts (z abs ∼ 2.5–3). These DLAs were originally selected from the presence of strong H2 lines directly seen at the DLA redshift in low-resolution low signal-to-noise ratio SDSS spectra. We confirm the detection of molecular hydrogen in all of them. We measure the column densities of H  i , H2 in various rotational levels, and metal species, and associated dust extinction. The metallicities, obtained from undepleted species, are in the range log  Z  = −0.8 to −0.2. We discuss the chemical enrichment in these clouds and compare their properties with that of other molecular-rich systems selected by other means. In particular, we show that three different methods of pre-selection of H2-bearing DLAs in the SDSS have their own biases but complement each other mostly in terms of chemical enrichment. We use the rotational excitation of H2 molecules together with the fine-structure energy levels of neutral carbon to constrain the physical conditions in the gas with the help of numerical modelling as well as analytical expressions for the surface density at which atomic to molecular conversion happens. We find that the H2-bearing medium revealed by the studied DLAs has typical values for the kinetic temperature, hydrogen density, and UV radiation field of T ∼ 100 K, n H ∼ 100 cm−3, and I UV , respectively, about twice the intensity of the Draine field. Detailed studies combining different selections should therefore bring important clues to understand the H  i -H2 transition at high redshift. [ABSTRACT FROM AUTHOR]

We present results from a search for strong H2 absorption systems proximate to quasars (zabs ≈ zem) in the Sloan Digital Sky Survey (SDSS) Data Release 14. The search is based on the Lyman-Werner band signature of damped H2 absorption lines without any prior on the associated metal or neutral hydrogen content. This has resulted in the detection of 81 systems with N(H2) ∼ 1019 − 1020 cm−2 located within a few thousand km s−1 from the quasar. Compared to a control sample of intervening systems, this implies an excess of proximate H2 systems by about a factor of 4 to 5. The incidence of H2 systems increases steeply with decreasing relative velocity, reaching an order of magnitude higher than expected from intervening statistics at Δv <  1000 km s−1. The most striking feature of the proximate systems compared to the intervening ones is the presence of Ly − α emission in the core of the associated damped H I absorption line in about half of the sample. This puts constraints on the relative projected sizes of the absorbing clouds to those of the quasar line emitting regions. Using the SDSS spectra, we estimate the H I, metal and dust content of the systems, which are found to have typical metallicities of one tenth Solar, albeit with a large spread among individual systems. We observe trends between the fraction of leaking Ly − α emission and the relative absorber-quasar velocity as well as with the excitation of several metal species, similar to what has been seen in metal-selected proximate DLAs. With the help of theoretical H I-H2 transition relations, we show that the presence of H2 helps to break the degeneracy between density and strength of the UV field as main sources of excitation and hence provides unique constraints on the possible origin and location of the absorbing clouds. We suggest that most of these systems originate from galaxies in the quasar group, although a small fraction of them could be located in the quasar host as well. We conclude that follow-up observations are still required to investigate the chemical and physical conditions in individual clouds and to assess the importance of AGN feedback for the formation and survival of H2 clouds. [ABSTRACT FROM AUTHOR]

We present the results of our automatic search for proximate damped Ly α absorption (PDLA) systems in the quasar spectra fromthe Sloan Digital Sky Survey Data Release 12. We constrain our search to those PDLAs lying within 1500 kms-1 from the quasar to make sure that the broad DLA absorption trough masks most of the strong Ly α emission from the broad-line region (BLR) of the quasar. When the Ly α emission from the BLR is blocked by these so-called eclipsing DLAs, narrow Ly α emission from the host galaxy could be revealed as a narrow emission line (NEL) in the DLA trough. We define a statistical sample of 399 eclipsing DLAs with log N(HI) ≥ 21.10. We divide our statistical sample into three subsamples based on the strength of theNEL detected in the DLA trough. By studying the stacked spectra of these subsamples, we found that absorptions from high ionization species are stronger in DLAs with stronger NEL in their absorption core.Moreover, absorption from the excited states of species like SiII are also stronger in DLAs with stronger NEL. We also found no correlation between the luminosity of the Ly α NEL and the quasar luminosity. These observations are consistent with a scenario in which the DLAs with stronger NEL are denser and physically closer to the quasar.We propose that these eclipsing DLAs could be the product of the interaction between infalling and outflowing gas. High-resolution spectroscopic observation would be needed to shed some light on the nature of these eclipsing DLAs. [ABSTRACT FROM AUTHOR]

We present a detailed study of the quasar-galaxy pair: J1243+4043-UGC 07904. The sight line of the background quasar (zq = 1.5266) passes through a region of the galaxy (zg = 0.0169) at an impact parameter of 6.9 kpc with high metallicity (0.5 Z⊙) and negligible dust extinction. We detect H I 21-cm absorption from the foreground galaxy at arcsecond and milliarcsecond scales. For typical cold neutral medium (CNM) temperatures in the Milky Way, this 21-cm absorber can be classified as a damped Lyα absorber (DLA). We infer the harmonic mean spin temperature of the gas to be ~400K and for a simple two-phase medium we estimate the CNM fraction to be fCNM = 0.27. This is remarkably consistent with the CNM fraction observed in the Galaxy and less than that of high-redshift DLAs. The quasar exhibits a core-jet morphology on milliarcsecond scales, corresponding to an overall extent of ~9 pc at zg. We show that the size of CNM absorbing clouds associated with the foreground galaxy is >5 pc and they may be part of cold gas structures that extend beyond ~35 pc. Interestingly, the rotation measure of quasar J1243+4043 is higher than any other source in samples of quasars with high-z DLAs. However, we do not find any detectable differences in rotation measures and polarization fraction of sight lines with or without high-z (z ≥ 2) DLAs or low-z (z ≤ 0.3) 21-cm absorbers. Finally, the foreground galaxy UGC07904 is also part of a galaxy group. We serendipitously detect H I 21-cm emission from four members of the group, and an ~80 kpc long HI bridge connecting two of the other members. The latter, together with the properties of the group members, suggests that the group is a highly interactive environment. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of an H2-rich, extremely strong intervening damped Ly α absorption system (DLA) at zabs = 2.786 towards the quasar J 0843+0221, observed with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. The total column density of molecular (resp. atomic) hydrogen is log N(H2) = 21.21 ± 0.02 (resp. log N(H I) = 21.82 ± 0.11), making it to be the first case in quasar absorption line studies with H2 column density as high as what is seen in 13CO-selected clouds in the Milky Way. We find that this system has one of the lowest metallicity detected among H2-bearing DLAs, with [Zn/H] = −1.52+0.08 −0.10. This can be the reason for the marked differences compared to systems with similar H2 column densities in the local Universe: (i) the kinetic temperature, T ∼ 120 K, derived from the J = 0, 1 H2 rotational levels is at least twice higher than expected; (ii) there is little dust extinction with AV < 0.1; (iii) no CO molecules are detected, putting a constraint on the XCO factor XCO > 2 × 1023 cm−2/(km s−1 K), in the very low metallicity gas. Low CO and high H2 contents indicate that this system represents 'CO-dark/faint' gas. We investigate the physical conditions in the H2-bearing gas using the fine-structure levels of C I, CII, Si II and the rotational levels of HD and H2. We find the number density to be about n ∼ 260–380 cm−3, implying a high thermal pressure of 3–5 × 104 cm−3 K.We further identify a trend of increasing pressure with increasing total hydrogen column density. This independently supports the suggestion that extremely strong DLAs (with log N(H)∼22) probe high-z galaxies at low impact parameters. [ABSTRACT FROM AUTHOR]

Broad absorption lines (BALs) found in a significant fraction of quasar spectra identify highvelocity outflows that might be present in all quasars and could be a major factor in feedback to galaxy evolution. Understanding the nature of these flows requires further constraints on their physical properties, including their column densities, for which well-studied BALs, such as CIV λλ1548,1551, typically provide only a lower limit because of saturation effects. Low abundance lines, such as P V λλ1118,1128, indicate large column densities, implying that outflows more powerful than measurements of C IV alone would indicate. We search through a sample of 2694 BAL quasars from the Sloan Digital Sky Survey III/Baryon Oscillation Spectroscopic Survey data release 9 quasar catalogue for such absorption, and we identify 81 ‘definite’ and 86 ‘probable’ detections of P V broad absorption, yielding a firm lower limit of 3.0–6.2 per cent for the incidence of such absorption among BAL quasars. The P V-detected quasars tend to have stronger C IV and Si IV absorption, as well as a higher incidence of LoBAL absorption, than the overall BAL quasar population. Many of the P V-detected quasars have C IV troughs that do not reach zero intensity (at velocities where P V is detected), confirming that the outflow gas only partially covers the UV continuum source. P V appears significantly in a composite spectrum of non-P V-detected BAL quasars, indicating that P V absorption (and large column densities) is much more common than indicated by our search results. Our sample of P V detections significantly increases the number of known P V detections, providing opportunities for follow-up studies to better understand BAL outflow energetics. [ABSTRACT FROM AUTHOR]

We report the discovery of the first ‘ghostly’ damped Ly α absorption system (DLA), which is identified by the presence of absorption from strong low-ion species at zabs = 1.704 65 along the line of sight to the quasar SDSS J113341.29−005740.0 with zem = 1.704 41. No Ly α absorption trough is seen associated with these absorptions because the DLA trough is filled with the leaked emission from the broad emission-line region of the quasar. By modelling the quasar spectrum and analysing the metal lines, we derive log N(H i)(cm−2) ∼21.0 ± 0.3. The DLA cloud is small (≤0.32 pc), thus not covering entirely the broad-line region and is located at ≥39 pc from the central active galactic nucleus (AGN). Although the DLA is slightly redshifted relative to the quasar, its metallicity ([S/H] = −0.41 ± 0.30) is intermediate between what is expected from infalling and outflowing gas. It could be possible that the DLA is part of some infalling material accreting on to the quasar host galaxy through filaments, and that its metallicity is raised by mixing with the enriched outflowing gas emanating from the central AGN. Current DLA surveys miss these ‘ghostly’ DLAs, and it would be important to quantify the statistics of this population by searching the Sloan Digital Sky Survey (SDSS) data base using metal absorption templates. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations of six high redshift (zem > 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate (zabs ~ zem) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ dLyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range -1.75 < [Si/H] < -0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Aliii/Siii ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments. [ABSTRACT FROM AUTHOR]

We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 (zCIV ~ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped Lyman α (DLA; logN(H I) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using CLOUDY models that explain the presence of strong N V and P V absorption together with the detection of Si II* and O I** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 < nH < 710 cm-3 and 580 > r0 > 230 pc, respectively. Sizes of the neutral (~2-9pc) and highly ionized phases (~3-80pc) are consistent with the partial coverage of the C IV BLR by the C IV absorption from the DLA (covering factor of ~0.85). We show that the residuals are consistent with emission from the NLR with C IV/Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ~500 km s-1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up. [ABSTRACT FROM AUTHOR]

We study the H2 molecular content in high redshift damped Lyman-alpha systems (DLAs) as a function of the Hı column density. We find a significant increase of the H2 molecular content around log N(Hı) (cm-2)~21.5-22, a regime unprobed until now in intervening DLAs, beyond which the majority of systems have log N(H2) > 17. This is in contrast with lines of sight towards nearby stars, where such H2 column densities are always detected as soon as log N(HI)>20.7. This can qualitatively be explained by the lower average metallicity and possibly higher surrounding UV radiation in DLAs. However, unlike in the Milky Way, the overall molecular fractions remain modest, showing that even at a large N(Hı) only a small fraction of overall Hı is actually associated with the self-shielded H2 gas. Damped Lyman-alpha systems with very high-N(Hı) probably arise along quasar lines of sight passing closer to the centre of the host galaxy where the gas pressure is higher. We show that the colour changes induced on the background quasar by continuum (dust) and line absorption (Hı Lyman and H2 Lyman & Werner bands) in DLAs with log N(Hı)~22 and metallicity ~1/10 solar is significant, but not responsible for the long-discussed lack of such systems in optically selected samples. Instead, these systems are likely to be found towards intrinsically fainter quasars that dominate the quasar luminosity function. Colour biasing should in turn be severe at higher metallicities. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of three extremely strong, intervening damped Lyman-α systems (ESDLAs, with log N(HI) ⩾ 21.7) observed towards quasars with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. We measure overall metallicities of [Zn/H] ~ -1.2, -1.3, and -0.7 at, respectively, Zabs = 2.34 towards SDSS J214043.02-032139.2 (log N(HI) = 22.4 ± 0.1), Zabs = 3.35 towards SDSS J145646.48+160939.3 (log N(HI) = 21.7 ± 0.1), and Zabs = 2.25 towards SDSS J015445.22+193515.8 (log N(HI) = 21.75 ± 0.15). Iron depletion of about a factor 15 compared to volatile elements is seen in the DLA towards J2140-0321, while the other two show deletion that is typical of known DLAs. We detect H2 towards J2140-0321 (log N(H2) = 20.13 ± 0.07) and J1456+1609 (log N(H2) = 17.10 ± 0.09) and argue for a tentative detection towards J0154+1935. Absorption from the excited fine-structure levels of O I, C I, and Si II are detected in the system towards J2140-0321, which has the largest HI column density detected so far in an intervening DLA. This is the first detection of O I fine-structure lines in a QSO-DLA, which also provides us with a rare possibility to study the chemical abundances of less abundant atoms like Co and Ge. Simple single-phase photo-ionisation models fail to reproduce all the observed quantities. Instead, we suggest that the cloud has a stratified structure: H2 and C I most likely stem from a dense (log nH ~ 2.5-3) and cold (80K) phase and from a warm (250 K) phase. They contain a fraction of the total HI,while a warmer (T > 1000 K) phase probably contributes significantly to the high excitation of O I fine-structure levels. The observed C I/H2 column density ratio is surprisingly low compared to model predictions, and we do not detect CO molecules: this suggests a possible underabundance of C by 0.7 dex compared to other alpha elements. The absorber could be a photo-dissociation region close to a bright star (or a star cluster) where higher temperature occurs in the illuminated region. Direct detection of on-going star formation through e.g. near-infrared emission lines in the surroundings of the gas would enable a detailed physical modelling of the system. [ABSTRACT FROM AUTHOR]

Chlorine and molecular hydrogen are known to be tightly linked together in the cold phase of the local interstellar medium through rapid chemical reactions. We present here the first systematic study of this relation at high redshifts using H2-bearing damped Lyα systems (DLAs) detected along quasar lines of sight. Using high-resolution spectroscopic data from VLT/UVES and Keck/HIRES, we report the detection of Cl?I in 9 DLAs (including five new detections) out of 18 high-z DLAs with N(H2) ≥ 1017.3 cm-2 (including a new H2 detection at z = 3.09145 towards J?2100-0641) and present upper limits for the remaining 9 systems. We find a ~5σ correlation between N(Cl?I) and N(H2) with only ~0.2 dex dispersion over the range 18.1 < log N(H2) < 20.1, thus probing column densities 10 times lower than those seen towards nearby stars, roughly following the relation N(Cl?I) ≈ 1.5 × 10-6 × N(H2). This relation between column densities is surprisingly the same at low and high redshift suggesting that the physical and chemical conditions are similar for a given H2 (or Cl?I) column density. In turn, the N(Cl I) /N(H2) ratio is found to be uncorrelated with the overall metallicity in the DLA. Our results confirm that neutral chlorine is an excellent tracer of molecule-rich gas and show that the molecular fraction and/or metallicity in the H2-bearing component of DLA could possibly be much higher than the line-of-sight average values usually measured in DLAs. [ABSTRACT FROM AUTHOR]

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, α. A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detailed test of this evidence. Towards that end, we observed equatorial quasar HS 1549+1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by ‘supercalibrating’ them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectra's wavelength scales which would have caused significant systematic errors in our α measurements. For each telescope we measure the relative deviation in α from the current laboratory value, Δα/α, in three absorption systems at redshifts zabs = 1.143, 1.342 and 1.802. The nine measurements of Δα/α are all consistent with zero at the 2σ level, with 1σ statistical (systematic) uncertainties 5.6–24 (1.8–7.0) parts per million (ppm). They are also consistent with each other at the 1σ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: Δα/α = −5.4 ± 3.3stat ± 1.5sys ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring Δα/α = −0.6 ± 1.9stat ± 0.9sys ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes. [ABSTRACT FROM PUBLISHER]

Context. Molecular hydrogen in the interstellar medium (ISM) of high-redshift galaxies can be detected directly from its UV absorption imprinted in the spectrum of background quasars. Associated absorption from Hi and metals allow for the study of the chemical enrichment of the gas, while the analysis of excited species and molecules make it possible to infer the physical state of the ISM gas. In addition, given the numerous H2 lines usually detected, these absorption systems are unique tools to constrain the cosmological variation of the proton-to-electron mass ratio, μ. Aims. We intend to study the chemical and physical state of the gas in the H2-bearing cloud at zabs = 2:658601 towards the quasar Q J 0643-5041 (zem = 3:09) and to derive a useful constraint on the variation of μ. Methods. We use high signal-to-noise ratio, high-resolution VLT-UVES data of Q J 0643-5041 amounting to a total of more than 23 h exposure time and fit the Hi, metals, and H2 absorption features with multiple-component Voigt profiles. We study the relative populations of H2 rotational levels and the fine-structure excitation of neutral carbon to determine the physical conditions in the H2-bearing cloud. Results. We find some evidence for part of the quasar broad-line emission region not being fully covered by the H2-bearing cloud. We measure a total neutral hydrogen column density of log N(H i)(cm-2) = 21:03 ± 0:08. Molecular hydrogen is detected in several rotational levels, possibly up to J = 7, in a single component. The corresponding molecular fraction is log f = -2:19+0:07 -0:08, where f = 2N(H2)/(2N(H2) + N(H i)). The H2 Doppler parameter is of the order of 1.5 km s-1 for J = 0, 1, and 2 and larger for J > 2. The molecular component has a kinetic temperature of Tkin ≃ 80 K, which yields a mean thermal velocity of ∼1 km s-1, consistent with the Doppler broadening of the lines. The UV ambient flux is of the order of the mean ISM Galactic flux.We discuss the possible detection of HD and derive an upper limit of log N(HD) ≲ 13:65±0:07 leading to log HD/(2 × H2) ≲ -5:19±0:07, which is consistently lower than the primordial D/H ratio. Metals span ∼210 km s-1 with [Zn/H] = -0:91 ± 0:09 relative to solar, with iron depleted relative to zinc [Zn/Fe] = 0:45 ± 0:06, and with the rare detection of copper. We follow the procedures used in our previous works to derive a constraint on the cosmological variation of μ, Δμ/μ = (7:4 ± 4:3stat ± 5:1syst) × 10-6. [ABSTRACT FROM AUTHOR]

Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, α, and the proton-to-electron mass ratio, μ = mp/me, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution ( R ≈ 60000) and high signal-to-noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. (2013) and Rahmani et al. (2013). A stringent bound for Δ α / α is obtained for the absorber at zabs = 1.6919 towards HE 2217-2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in α in this system is +1.3 ± 2.4stat ± 1.0sys ppm if Al II λ 1670 Å and three FeII transitions are used, and +1.1 ± 2.6stat ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on α -variation from an individual absorber and reveals no evidence for variation in α at the 3-ppm precision level (1 σ confidence). The expectation at this sky position of the recently-reported dipolar variation of α is (3.2-5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δ α / α at face value is not supporting this expectation but not inconsistent with it at the 3 σ level. For the proton-to-electron mass ratio the analysis of the H2 absorption lines of the zabs ≈ 2.4018 damped Ly α system towards HE 0027-1836 provides Δ μ / μ = (-7.6 ± 8.1stat ± 6.3sys) ppm which is also consistent with a null variation. The cross-correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter-order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We report the detection of 21-cm absorption from foreground galaxies towards quasars, specifically zgal = 0.3120 towards SDSS J084957.97+510829.0 (zqso = 0.584; Pair-I) and zgal = 0.3714 towards SDSS J144304.53+021419.3 (zqso = 1.82; Pair-II). In both the cases, the integrated 21-cm optical depth is consistent with the absorbing gas being a damped Lyman-α (DLA) system. In the case of Pair-I, strong Na i and Ca ii absorption lines are also detected at zgal in the QSO spectrum. We identify an early-type galaxy at an impact parameter of b ~ 14 kpc whose photometric redshift is consistent with that of the detected metal and 21-cm absorption lines. This would be the first example of an early-type galaxy associated with an intervening 21-cm absorber. The gas detected in 21-cm and metal absorption lines on the outskirts of this luminous red galaxy could be associated with the reservoir of cold Hi gas with a low level of star formation activity in the outer regions of the galaxy as reported in the literature for z ~ 0.1 earlytype galaxies. In the case of Pair-II, the absorption is associated with a low surface brightness galaxy that, unlike most other known quasar-galaxy pairs (QGPs), i.e. QSO sight lines passing through disks or halos of foreground galaxies, is identified only via narrow optical emission lines detected on top of the QSO spectra. Using SDSS spectra we infer that the emission lines originate within ~5 kpc of the QSO sight line, and the gas has metallicity [12+O/H] ~ 8.4 and star formation rate ~0.7-0.8 M☉ yr-1. The measured 21-cm optical depth can be reconciled with the N(H I) we derive from the measured extinction (AV = 0.6) if either the H I gas is warm or the extinction per hydrogen atom in this galaxy is much higher than the mean value of the Small Magellanic Cloud. Finally, using a sample of 9 QGPs with 21-cm absorption detection from our observations and literature, we report a weak anti-correlation (Spearman rank, rs = -0.3) between the 21-cm optical depth and galaxy impact parameter. Milliarcsecond scale images and spectra are required to understand the implications of this. [ABSTRACT FROM AUTHOR]

ABSTRACT We present high-resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope and 21-cm absorption spectra obtained with the Giant Metrewave Radio Telescope and the Green Bank Telescope of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsecond-scale radio images of these quasars obtained with the Very Large Baseline Array. We use the data on four of these systems to constrain the time variation of x ≡ gpα2/μ, where gp is the proton gyromagnetic factor, α is the fine structure constant and μ is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In both cases, we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Δ x/ x to be, respectively, −(0.1 ± 1.3) × 10−6 and (0.0 ± 1.5) × 10−6 at the mean redshift of 〈 z〉 = 1.36 corresponding to a look-back time of ∼9 Gyr. This is the most stringent constraint ever obtained on Δ x/ x. If we only use the two systems towards quasars unresolved at milliarcsecond scales, we get the simple mean of Δ x/ x = +(0.2 ± 1.6) × 10−6. Assuming the constancy of other constants, we get Δα/α = (0.0 ± 0.8) × 10−6, which is a factor of 2 better than the best constraints obtained so far using the many-multiplet method. On the other hand, assuming that α and gp have not varied we derive Δμ/μ = (0.0 ± 1.5) × 10−6 which is again the best limit ever obtained on the variation of μ over this redshift range. Using independent constraints on Δα/α at z < 1.8 and Δμ/μ at z ∼ 0.7 available in the literature, we get Δ gp/ gp ≤ 3.5 × 10−6(1σ). [ABSTRACT FROM AUTHOR]

We report four new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of 17 strong (rest equivalent width, Wr(Mg iiλ2796) ⩾ 1 Å) intervening Mg ii absorbers at 0.5 < zabs < 1.5. We also present 20-cm milliarcsecond scale maps of 40 quasars having 42 intervening strong Mg ii absorbers for which we have searched for 21-cm absorption. These maps are used to understand the dependence of 21-cm detection rate on the radio morphology of the background quasar and address the issues related to the covering factor of absorbing gas. Combining 21-cm absorption measurements for 50 strong Mg ii systems from our surveys with the measurements from literature, we obtain a sample of 85 strong Mg ii absorbers at 0.5 < zabs < 1 and 1.1 < zabs < 1.5. We present detailed analysis of this 21-cm absorption sample, taking into account the effect of the varying 21-cm optical depth sensitivity and covering factor associated with the different quasar sight lines. We find that the 21-cm detection rate is higher towards the quasars with flat or inverted spectral index at cm wavelengths. About 70% of 21-cm detections are towards the quasars with linear size, LS < 100 pc. The 21-cm absorption lines having velocity widths, ΔV > 100 km s-1 are mainly seen towards the quasars with extended radio morphology at arcsecond scales. However, we do not find any correlation between the integrated 21-cm optical depth, ∫ τdv, or the width of 21-cm absorption line, ΔV, with the LS measured from the milliarcsecond scale images. All this can be understood if the absorbing gas is patchy with a typical correlation length of ∼30-100 pc. We confirm our previous finding that the 21-cm detection rate for a given optical depth threshold can be increased by up to a factor 2 by imposing the following additional constraints: Mg ii doublet ratio <1.1, W(Mg ii)/W(Fe ii) < 1.47 and W(Mg i)/W(Mg ii) > 0.27. This suggests that the probability of detecting 21-cm absorption is higher in the systems with high N(H i). We show that within the measurement uncertainty, the 21-cm detection rate in strong Mg ii systems is constant over 0.5 < zabs < 1.5, i.e., over ∼30% of the total age of universe. We show that the detection rate can be underestimated by up to a factor 2 if 21-cm optical depths are not corrected for the partial coverage estimated using milliarcsecond scale maps. Since stellar feedback processes are expected to diminish the filling factor of cold neutral medium over 0.5 < z < 1, this lack of evolution in the 21-cm detection rate in strong Mg ii absorbers is intriguing. Large blind surveys of 21-cm absorption lines with the upcoming Square Kilometre Array pathfinders will provide a complete view of the evolution of cold gas in galaxies and shed light on the nature of Mg ii systems and DLAs, and their relationship with stellar feedback processes. [ABSTRACT FROM AUTHOR]

ABSTRACT We study the time variability of five Fe low-ionization broad absorption line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2-m telescope at IUCAA Girawali Observatory (IGO) spanning an interval of up to 10 years. We report a dramatic variation in the Al iii and Fe iii fine-structure lines in the spectra of SDSS J221511.93−004549.9 ( zem∼ 1.478). However, there is no such strong variability shown by the C iv absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe iii absorption being stronger than Fe ii and (iii) the apparent ratio of Fe iii UV 48 to Fe iii UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe iii fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between 2000 and 2008. Using the template-fitting techniques, we show that the apparent inversion of the strength of ultraviolet lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to a change in the ionization state of the gas or due to the transverse motion of this absorbing gas. The shortest variability time-scale of Al iii line gives a lower limit on the electron density of the absorbing gas as cm−3. The remaining four FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93−004549.9 shows significant (≥0.2 mag) variability. [ABSTRACT FROM AUTHOR]

We study the time variability of five Fe low-ionization broad absorption line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2-m telescope at IUCAA Girawali Observatory (IGO) spanning an interval of up to 10 years. We report a dramatic variation in the Al iii and Fe iii fine-structure lines in the spectra of SDSS J221511.93−004549.9 (zem∼ 1.478). However, there is no such strong variability shown by the C iv absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe iii absorption being stronger than Fe ii and (iii) the apparent ratio of Fe iii UV 48 to Fe iii UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe iii fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between 2000 and 2008. Using the template-fitting techniques, we show that the apparent inversion of the strength of ultraviolet lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to a change in the ionization state of the gas or due to the transverse motion of this absorbing gas. The shortest variability time-scale of Al iii line gives a lower limit on the electron density of the absorbing gas as cm−3. The remaining four FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93−004549.9 shows significant (≥0.2 mag) variability. [ABSTRACT FROM AUTHOR]

We report the detection of neutral deuterium in the low-metallicity damped Lyman-α system at zabs = 2.621 towards the quasar CTQ 247. Using a high signal-to-noise and high spectral resolution (R = 60   000) spectrum from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we precisely measure the deuterium-to-oxygen ratio log N(D Ι)/N(O ɪ) = 0.74 ± 0.04, as well as the overall oxygen abundance, log N(O ɪ/N(H ɪ) = -5.30 ± 0.10 (or equivalently [O/H] = -1.99 ± 0.10 with respect to the solar value). Assuming uniform metallicity throughout the system, our measurement translates into (D/H) = (2.8-0.6+0.8) × 10-5. This ratio is consistent within errors (<0.4σ) with the primordial ratio, (D/H)p = (2.59 ± 0.15) × 10-5, predicted by standard Big-Bang nucleosynthesis using the WMAP7 value of the cosmological density of baryons (100 Ωbh² = 2.249 ± 0.056). The D ɪ absorption lines are observed to be broader than the O ɪ absorption lines. From a consistent fit of the profiles we derive the turbulent broadening to be 5.2 km s-1 and the temperature of the gas to be T = 8800 ± 1500 K, corresponding to a warm neutral medium. [ABSTRACT FROM AUTHOR]

We report the detection of 21-cm and molecular hydrogen absorption lines in the same damped Lyman α system (DLA; with log N(H i) = 21.36 ± 0.10) at towards SDSS J133724.69+315254.55 ( ). We estimate the spin temperature of the gas to be K, intermediate between the expected values for cold and warm neutral media. This suggests that the H i absorption originates from a mixture of different phases. The total molecular fraction is low, , and H2 rotational level populations are not in equilibrium. The average abundance of the α-elements is [S/H]= . Nitrogen and iron are found underabundant with respect to α-elements by ∼1.0 and ∼0.5 dex, respectively. Using photoionization models we conclude that the gas, of mean density , is located more than 270 kpc away from the quasi-stellar object. While the position of the 21-cm absorption line coincides with the H2 velocity profile, its centroid is shifted by with respect to the redshift measured from the H2 lines. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km s−1. From this, we constrain the variation of the combination of fundamental constants . This system is unique as we can at the same time have an independent constraint on μ using H2 lines. However, as the H2 column density is low, only Werner band absorption lines are seen and, unfortunately, the range of sensitivity coefficients is too narrow to provide a stringent constraint: . The Ultraviolet and Visual Echelle Spectrograph spectrum reveals another DLA at with log N(H i) = 20.41 ± 0.15 and low metallicity, [Si/H]= , in which [O/C] and [O/Si]∼ 0. This shows that even in the very early stages of chemical evolution, the carbon or silicon to oxygen ratios can be close to solar. Using Voigt profile fitting we derive log( N(D i)/ N(H i)) = in this system. This is a factor of 2 smaller than the value expected from the best-fitting value of Ωb from the Wilkinson Microwave Anisotropy Probe 5-yr data. This confirms the presence of astration of deuterium even at very low metallicity. [ABSTRACT FROM AUTHOR]

We present the results of a systematic Giant Metrewave Radio Telescope (GMRT) survey of 21-cm absorption in a representative and unbiased sample of 35 strong Mg ii systems in the redshift range: , 33 of which have . The survey using ∼400 h of telescope time has resulted in nine new 21-cm detections and stringent 21-cm optical depth upper limits (median 3σ optical depth per 10 km s−1 of 0.017) for the remaining 26 systems. This is by far the largest number of 21-cm detections from any single survey of intervening absorbers. Prior to our survey, no intervening 21-cm system was known in the above redshift range, and only one system was known in the redshift range . We discuss the relation between the detectability of 21-cm absorption and various properties of UV absorption lines. We show that if Mg ii systems are selected with the following criteria, Mg ii doublet ratio ≤1.3 and Wr(Mg i)/ Wr(Mg ii) ≥ 0.3, then a detection rate of 21-cm absorption up to 90 per cent can be achieved. We estimate n21, the number per unit redshift of 21-cm absorbers with and integrated optical depth , and show that n21 decreases with increasing redshift. In particular, for and falls by a factor of 4 from to . The evolution seems to be stronger for stronger Mg ii systems. Using a subsample of systems for which high-frequency Very Long Baseline Array (VLBA) images are available, we show that the effect is not related to the structure of the background radio sources and is most probably due to the evolution of the cold neutral medium filling factor in Mg ii systems. We find no correlation between the velocity spread of the 21-cm absorption feature and Wr(Mg ii) at . [ABSTRACT FROM AUTHOR]

We have discovered two dusty intervening Mg ii absorption systems at in the Sloan Digital Sky Survey (SDSS) data base. The overall spectra of both quasi-stellar objects (QSOs) are red and are well modelled by the composite QSO spectrum reddened by the extinction curve from the Large Magellanic Cloud (LMC2) Supershell redshifted to the rest frame of the Mg ii systems. In particular, we detect clearly the presence of the ultraviolet (UV) extinction bump at Å. Absorption lines of weak transitions like Si iiλ1808, Cr iiλ2056, Cr ii+ Zn iiλ2062, Mn iiλ2594, Ca iiλ3934 and Ti iiλ1910 from these systems are detected even in the low signal-to-noise ratio and low-resolution SDSS spectra, suggesting high column densities of these species. The depletion pattern inferred from these absorption lines is consistent with that seen in the cold neutral medium of the LMC. Using the LMC versus N(H i) relationship, we derive N(H i) in both systems. Metallicities are close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these two relatively weak radio QSOs resulted in the detection of 21-cm absorption in both the cases. We show that the spin temperature of the gas is of the order of or smaller than 500 K. These systems provide a unique opportunity to search for molecules and diffuse interstellar bands at . [ABSTRACT FROM AUTHOR]

We investigate how well the three-dimensional density field of neutral hydrogen in the intergalactic medium (IGM) can be reconstructed using the Lyman α absorptions observed along lines-of-sight to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. The global statistical and topological properties of the recovered field are analysed quantitatively through the power spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of interskeleton distance. As a consequence of the nearly lognormal nature of the density distribution at the scales under consideration, the tomography is best carried out on the logarithm of the density rather than the density itself. At scales larger than ∼1.4 〈 dLOS〉, where 〈 dLOS〉 is the mean separation between lines-of-sight, the reconstruction accurately recovers the topological features of the large-scale density distribution of the gas, in particular the filamentary structures: the interskeleton distance between the reconstruction and the exact solution is smaller than 〈 dLOS〉. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered H i density field matches well that of the original one and the low-order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20 per cent for a mean line-of-sight separation smaller than ∼2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the lognormal behaviour that are ascribed to highly non-linear objects in overdense regions. [ABSTRACT FROM AUTHOR]

We study the density field around quasars using high-quality medium spectral resolution Echelle Spectrograph and Imager–Keck spectra ( , signal-to-noise ratio (S/N) > 25) of 45 high-redshift quasars selected from a total of 95 spectra. This large sample considerably increases the statistics compared to previous studies. The redshift evolution of the mean photoionization rate and the median optical depth of the intergalactic medium (IGM) are derived statistically from the observed transmitted flux and the pixel optical depth probability distribution function, respectively. This is used to study the so-called proximity effect, that is, the observed decrease of the median optical depth of the IGM in the vicinity of the quasar caused by enhanced photoionization rate due to photons emitted by the quasar. We show that the proximity effect is correlated with the luminosity of the quasars, as expected. By comparing the observed decrease of the median optical depth with the theoretical expectation, we find that the optical depth does not decrease as rapidly as expected when approaching the quasar if the gas in its vicinity is part of the standard IGM. We interpret this effect as revealing gaseous overdensities on scales as large as Mpc. The mean overdensity is of the order of 2 and 5 within, respectively, 10 and Mpc. If true, this would indicate that high-redshift quasars are located in the centre of overdense regions that could evolve with time into massive clusters of galaxies. The overdensity is correlated with luminosity: brighter quasars show higher overdensities. [ABSTRACT FROM AUTHOR]

We present the transverse flux correlation function of the Lyα forest in quasar absorption spectra at from VLT-FORS and VLT-UVES observations of a total of 32 pairs of quasars; 26 pairs with separations in the range and six pairs with . Correlation is detected at the 3σ level up to separations of the order of ∼4 arcmin (or comoving at for and ). We have, furthermore, measured the longitudinal correlation function at a somewhat higher mean redshift from 20 lines of sight observed with high spectral resolution and high signal-to-noise ratio with VLT-UVES. We compare the observed transverse and longitudinal correlation functions to that obtained from numerical simulations and illustrate the effect of spectral resolution, thermal broadening and peculiar motions. The shape and correlation length of the correlation functions are in good agreement with those expected from absorption by the filamentary and sheet-like structures in the photoionized warm intergalactic medium predicted in cold dark matter (CDM)-like models for structures formation. Using a sample of 139 C iv systems detected along the lines of sight towards the pairs of quasars we also investigate the transverse correlation of metals on the same scales. The observed transverse correlation function of intervening C iv absorption systems is consistent with that of a randomly distributed population of absorbers. This is likely due to the small number of pairs with separation less than 2 arcmin. We detect, however, a significant overdensity of systems in the sightlines towards the quartet Q 0103−294A&B, Q 0102−2931 and Q 0102−293 which extends over the redshift range and an angular scale larger than 10 arcmin. [ABSTRACT FROM AUTHOR]

We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with and 316 Mg ii and 82 Fe ii absorption components with in 19 high signal-to-noise ratio (60–100 pixel−1), high-resolution quasar spectra. C iv and Si iv trace each other closely and their line-of-sight correlation functions exhibit a steep decline at large separations and a flatter profile below ≈150 km s−1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ( v) increases with time over the redshift range detected (1.5–3). Carrying out a detailed smoothed particle hydrodynamic simulation ( comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity ( . However, the properties of are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass . We derive best-fitting values of comoving Mpc and at . Our lower-redshift (0.5–2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the measurements, and the turnover is shifted to somewhat smaller distances, ≈75 km s−1. Again, these features do not change with column density, but there are hints that the amplitudes of and increase with time. We describe an analytic ‘bubble’ model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best-fitting values of and . Equally good analytic fits to all four species are found in a similarly biased high-redshift enrichment model in which metals are placed within 2.4 comoving Mpc of sources at . [ABSTRACT FROM AUTHOR]

ABSTRACT We study the clustering of matter in the intergalactic medium from the Lyman α forests seen in the spectra of pairs or groups of z∼ 2 quasars observed with FORS2 and UVES at the VLT-UT2 Kueyen ESO telescope. The sample consists of five pairs with separation of 0.6, 1, 2.1, 2.6 and 4.4 arcmin and a group of four quasars with separations from 2 up to 10 arcmin. This unprecedented data set allows us to measure the transverse flux correlation function for a range of angular scales. Correlations are clearly detectable at separations smaller than 3 arcmin. The shape and correlation length of the transverse correlation function on these scales are in good agreement with those expected from absorption by the photoionized warm intergalactic medium associated with the filamentary and sheet-like structures predicted in cold dark matter-like models for structure formation. At larger separation no significant correlation is detected. Assuming that the absorbing structures are randomly orientated with respect to the line of sight, the comparison of transverse and longitudinal correlation lengths constrains the cosmological parameters (as a modified version of the Alcock & Paczynski test). The present sample is too small to have significant constraints. Using N-body simulations, we investigate the possibility of constraining Ω[sub Λ] from future larger samples of quasistellar object pairs with similar separations. The observation of a sample of 30 pairs at 2, 4.5 and 7.5 arcmin should constrain the value of Ω[sub Λ] at ±15 per cent (2σ level). We also use the observed spectra of the group of four quasars to search for underdense regions in the intergalactic medium. We find a quasi-spherical structure of reduced absorption with radius 12.5 h[sup -1] Mpc , which we identify as an underdense region. [ABSTRACT FROM AUTHOR]

We discuss the implementation of Bayesian inversion methods in order to recover the properties of the intergalactic medium from observations of the neutral hydrogen Lyman α absorptions observed in the spectra of high-redshift quasars (the so-called Lyman α forest). We use two complementary schemes: (i) a constrained Gaussian random field linear approach, and (ii) a more general non-linear explicit Bayesian deconvolution method, which offers in particular the possibility to constrain the parameters of the equation of state for the gas. The interpolation ability of the first approach is shown to be equivalent to the second one in the limit of negligible measurement errors, low-resolution spectra and null mean prior. While relying on prior assumption for the two-point correlation functions, we show how to recover, at least qualitatively, the three-dimensional topology of the large-scale structures in redshift space by inverting a suitable network of adjacent, low-resolution lines of sight. The methods are tested on regular bundles of lines of sight using N-body simulations specially designed to tackle this problem. We also discuss the inversion of single lines of sight observed at high spectral resolution. Our preliminary investigations suggest that the explicit Bayesian method can be used to derive quantitative information on the physical state of the gas when the effects of redshift distortion are negligible. The information in the spectra remains degenerate with respect to two parameters (the temperature scale factor and the polytropic index) describing the equation of state of the gas. Redshift distortion is considered by simultaneous constrained reconstruction of the velocity and the density field in real space, while assuming statistical correlation between the two fields. The method seems to work well in the strong prior régime where peculiar velocities are assumed to be the most likely realization in the density field. Finally, we investigate the effect of line-of-sight separation and number of lines of sight. Our analyses suggest that multiple low-resolution lines of sight could be used to improve the most likely velocity reconstruction on a high-resolution line of sight. [ABSTRACT FROM AUTHOR]

A correction to the article "The Sources of Intergalactic Metals" that was published in the March 2006 issue is presented.

ABSTRACT We study the time variability of five Fe low-ionization broad absorption line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2-m telescope at IUCAA Girawali Observatory (IGO) spanning an interval of up to 10 years. We report a dramatic variation in the Al iii and Fe iii fine-structure lines in the spectra of SDSS J221511.93−004549.9 ( zem∼ 1.478). However, there is no such strong variability shown by the C iv absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe iii absorption being stronger than Fe ii and (iii) the apparent ratio of Fe iii UV 48 to Fe iii UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe iii fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between 2000 and 2008. Using the template-fitting techniques, we show that the apparent inversion of the strength of ultraviolet lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to a change in the ionization state of the gas or due to the transverse motion of this absorbing gas. The shortest variability time-scale of Al iii line gives a lower limit on the electron density of the absorbing gas as cm−3. The remaining four FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93−004549.9 shows significant (≥0.2 mag) variability. [ABSTRACT FROM AUTHOR]